1. Field of the Invention
The present invention relates, in general, to a printed circuit board (PCB) having an inductor and a method of fabricating the same and, more particularly, to a PCB having an inductor, in which the inductor is formed by appropriately arranging spiral vertical structures so as to effectively use the space of the PCB, and a method of fabricating the same.
2. Description of the Prior Art
Used in electric and electronic circuits, a passive component is generally classified into a resistor, a capacitor, and an inductor. Of them, the capacitor and the inductor are the most basic components capable of storing and supplying energy. Since they have frequency characteristics, their materials depend on frequency, voltage, and electric current.
Meanwhile, current electronic devices are becoming small, light, and slim, and advances in fabrication and design technologies of the electronic devices promote miniaturization of the passive components used in the electronic devices. Particularly, miniaturization of the capacitor and the inductor is an important factor for determining the size of a product.
Unlike other passive components, the inductor is not fabricated as a ready-made product except in the very unusual case when the inductor is used for low power signals. Accordingly, the inductor is obtained through many steps of design, fabrication, test, evaluation, outsourcing and the like.
When two or more inductors are simultaneously connected to one core, the resulting structure acts as a transformer. The transformer is an important device which is used for electric insulation, impedance transformation, magnitude transformation of electric voltage and current, and filtering.
The inductor and the transformer have basically the same structure, in which they are wound around the core, but they are significantly different from each other in application.
The conventional inductor used in integrated circuit (IC) packages or printed circuit boards (PCBs) has a 2-D type structure in which micro-strips are layered on an external layer of a substrate. This inductor may be fabricated using patterns, such as micro-strips, while the patterns are formed long and straight. However, the inductor is mainly fabricated in one of the three types shown in FIG. 1 because of spatial limitations.
In the three types of inductors, the pattern is twisted so as to be formed long in a narrow space. Of them, a spiral inductor is frequently used because it is useful to form a long pattern. The spiral inductor is advantageous in that since it spirals in one direction while forming concentric circles, magnetic fields are added in the same direction by mutual inductance. Thereby, it is possible to form high inductance in the small area.
A meander line inductor winds and twists like a snake. However, the meander line inductor is disadvantageous in that since mutual inductances are generated in opposite directions and thus offset each other, it is difficult to form high inductance for a given size. A loop inductor has shape and performance that are poorer than the two preceding types, thus it is seldom used, but is employed as a filter sometimes.
Of the three types of inductor, the spiral inductor is most advantageous, but is problematic in that the two-dimensional spiral inductor occupies too large an area of the substrate to be applicable to miniaturized and complicated electronic current devices while insufficient inductance is assured.
To avoid the above disadvantages, Japanese Patent Laid-Open Publication No. 2002-324962 discloses a PCB having an inductor and a method of fabricating the same.
With respect to this, two types of inductor structures are provided. The first type is shown in FIGS. 2a and 2b, in which conductor wires 22a and conductor wires 26a are electrically connected using via holes 25 formed through an insulating layer 23, thereby creating inductor parts, resulting in the embedding of the inductor in the PCB.
In FIG. 2a, the insulating layer is omitted. In the method of fabricating the PCB, as shown in FIGS. 3a to 3f, a copper foil layer is layered on a first insulating layer 21 to form a conductor layer 22 (refer to FIG. 3a), a predetermined resister pattern is formed on the conductor layer 22, the conductor layer 22 is etched using the resister pattern as a mask, and the resister pattern is separated to form first conductor wires 22a (refer to FIG. 3b).
Additionally, a second insulating layer 23 is formed on the first insulating layer 21, on which the first conductor wires 22a have already been formed (refer to FIG. 3c), holes 24 are formed through the second insulating layer 23 at predetermined positions (refer to FIG. 3d), and the holes 24 are packed to form a via hole 25 and a conductor layer 26 is formed, by electroless and electrolytic copper plating processes (refer to FIG. 3e). The conductor layer 26 is patterned to form second conductor wires 26a, inductor parts are formed (refer to FIG. 3f), and wires and via holes are simultaneously formed on other substrates, thereby creating the PCB having the inductor.
The second type is shown in FIG. 4, in which ring-shaped conductor wires 31, 32, and 33 are formed on insulating layers (not shown), and are electrically connected to each other through via holes 41, 42, thereby creating an inductor. In the method of fabricating the PCB having the inductor, a terminal electrode 31b of the first ring-shaped conductor wire 31, which is formed on the first insulating layer, and a terminal electrode 32a of the second ring-shaped conductor wire 32, which is formed on the second insulating layer, are electrically connected through the via hole 41 formed through the second insulating layer. As well, a terminal electrode 32b of the second ring-shaped conductor wire 32, which is formed on the second insulating layer, and a terminal electrode 33a of the third ring-shaped conductor wire 33, which is formed on the third insulating layer, are electrically connected through the via hole 42 formed through the third insulating layer, thereby creating the inductor. As described above, the ring-shaped conductor wires are electrically connected through the via holes formed through the insulating layers, and the desired number of resulting layers are laminated, thereby forming inductor parts. Wires and via holes are simultaneously formed on other insulating layers, thereby creating the PCB having the inductor.
With respect to this, an inductor structure according to another conventional technology is disclosed in Japanese Patent Laid-Open Publication No. 2003-209331, entitled “a PCB and a method of fabricating the same”.
A description will be given of other conventional technologies with reference to FIGS. 5 to 9. FIG. 5 illustrates a PCB according to another conventional technology, which shows a surface of a portion of the PCB including an inductor. As shown in FIG. 5, an inductor 51, which includes upper and lower wires, an insulating layer interposed between the upper and lower wires, and via holes for electrically connecting the upper and lower wires to each other therethrough, is embedded in the PCB. The PCB is provided with the inductor 51 and different resins, and the different resins consist of a resin 52 containing a magnetic substance and a resin 53 not containing the magnetic substance.
FIG. 6 is a sectional view taken along the line A–A′ of FIG. 5, and FIG. 7 is a sectional view taken along the line B–B′ of FIG. 5. As shown in FIGS. 6 and 7, a first insulating resin layer 54 is formed on a substrate 56, on which a wire pattern (not shown) is formed, and a second insulating resin layer 55 is formed thereon. The second insulating resin layer 55 is processed using an excimer laser to remove a portion thereof, through which the inductor is to be formed, and resin around the removed portion. Thereby, a groove is formed through the second insulating resin layer so that a lower wire 58 is exposed. A resin 52 containing a magnetic substance is packed in the groove and an upper wire 62 is then formed. In this case, the magnetic substance may be formed only between the via holes.
In a modified embodiment of FIG. 5, FIG. 8 is a sectional view taken along the line A–A′ of the PCB of FIG. 5, in which a magnetic substance is provided in the first insulating resin layer 54 of FIG. 5. In this case, a conductor insulating layer 59 is formed in advance on a substrate 56 so as to have a larger area than a punched portion, thereby forming a first insulating resin layer. After a lower wire 58 is formed, a groove is formed using a low-priced carbon dioxide gas laser instead of the excimer laser so that a surface of the first insulating resin layer is exposed.
In this regard, the insulating resin 59 and the lower wire 58 act as a stopper, and a portion of the resin, on which the lower wire 58 is not formed, is melted by the carbon dioxide gas laser, thereby forming the groove so that the conductor insulating layer 59 on the substrate is exposed. After the formation of the groove, the second insulating resin layer is formed. The subsequent procedure is the same as in FIGS. 6 and 7.
Furthermore, in another modified embodiment of FIG. 5, as shown in FIG. 9, a first insulating resin layer is formed through the same procedure as FIGS. 6 and 7. After an upper wire 62 is formed, a groove is formed using a carbon dioxide gas laser, and a resin containing a magnetic substance is packed in the groove. In this case, the upper wire 62 and a lower wire 58 are used as a stopper to form the groove.
Thereby, a PCB, in which a resin under the upper wire of the inductor is different from a resin on the lower wire, is created.
However, in the above prior arts, even though the spiral inductor is most advantageous, the spiral inductor is problematic in that it occupies too large an area of a substrate to be applied to miniaturized and complicated current electronic devices, and thus insufficient inductance is assured.